Dyeing of aluminum oxide coatings



This invention relates to the dyeing of oxidecoatings on aluminurnuor its alloys and has particular reference I to the obtaining of improved light fastness of such dyed coatings.

It is well known that' porous oxidecoatings formed on aluminumor its alloys are capable of absorbing dyes which may beret'ained most effectively in the coatings by "Qsealing. Dye absorbing coatings may be' produced in various known fashions by anodizing or chemical oxidation of the aluminum or aluminum alloy surfaces. In contrast, relatively non-absorbent oxide coatings may be produced by other oxidizing operations, including anodizing in various baths. When dyeing is to be effected, of course, absorbent coatings are desired and then sealing becomes important. The dyed coatings exhibit widely variable characteristics with respect to light fastness, and this has limited very considerably the dyes which are practical for such use. In particular, anthraquinone dyes of certaintypes'(more specifically referred to hereafter) would be highly desirable but have exhibited unsatisfactory charcteristics from the standpoint of light fastness, and the present invention isparticularly directed to procedures for the use of such dyes in a practical way. It may be here noted that the light ,fastness of dyed aluminum oxide coatings is not necessarily related to the light fastness of the dyes as used in other dyeing operations.

I have discovered that such-dyes may be-used to form 'coloredoxide coatings on aluminum and aluminum alloys which are resistant to fading by the adoption of procedures which may be generally described as-follows:

(1) A dye bath may-have addedv to itahydrolyzable salt of a 'weak metallic base, such salts being typically nickel acetate or ferric ammonium oxalate. The coated nited Stat P 2,927,872 Fatent'ed' Mar. 8, 1960 01 numbers, PR numbers, or names and manufacturers where numbers have apparently not be assigned:

or 1,027 (Alizarin Vl) CI 1034 (Alizarin Red S) CI 1053 (Alizarin Saphirol SE) ,CI 1054 (Alizarin Saphirol B) CI1073 (Alizarian Irisol R) CI 1078 (Alizarin Cyanine Green) CI.1085 (Alizarin Blue Black B) PR4-Calcochrome Brown PG PRlO-Erie Anthracene Brill. Blue 2GL Conc.

PR1 1-Alizarine Sapphire AR PR12-Calcocid Alizarine Blue 5 BA PR14-Calcochrome Brown G.B.

PR206--Pontachrome Fast Gray L. Conc. I

PR330Gycolan Yellow BEL 200% PR391-Gycolan Red GRL 200% Ahcoquinon Brilliant Cyanine Green (Arnold Hoffman & Co., Inc.) 1

Anthraquinone Blue 4 GL (E. I. Du Pont. de Nemours & Co., Inc.)

Anthraquinone Blue 2 GA (E. I. Du Pont de Nemours & Co., Inc.)

Anthraquinone Milling Blue BL (E. I. Du Pont de Nemours & Co., Inc.)

Anthraquinone Blue RA (E. I. Du Pont de Nemours &

Brilliant Alizarin Milling Blue BL (Sandoz Chemical aluminum (which term will be hereafter used to include I aluminum alloys) is treated at an elevated temperature with the dye bath, suchias at 120 F. for a period of a few minutes. This is followed by sealing usingas a seal hydrolyzable salt of a weak metallic base, thefsealing salt being also typically nickel acetate or ferric ammonium oxalate.

result, from the standpoint of light fastness, is startlingly different from that obtained by dyeing without the weak metallic base followed by sealing of the type just mentioned. V

(2) However, by the use of a special seal containing nickel acetate and a soluble fluoride, the initial dyeing may' be carried out in a bath which does not contain a hydrolyzable metallic salt.

While the same metallic salt may be incor-' porated in the dye bath and also used for sealing, the

practice of the invention, reference may -be-ma'de to the 1' Works, Inc.)

When these dyes are used various dyes ofother watersoluble types may be used for tint variations. Among these, andfound particularly useful, are:

01 4o (Alizarin Yellow R) PR 143 (Chromalon Black N.W.A. Conc.)

As specific examples of the practice of the invention, there may be cited the following:

Dyeing of an absorbent oxide film on aluminum (produced, for example, byanodizing the metal in an 18% by weight aqueous solution of sulfuric acid at 12 amperes per square foot, alternating current, at F. for 15 minutes) is effected in an aqueous solution of 20 grams per liter of ferric ammonium oxalate and 5 grams per liter of the dye CI 1053 to which a small .amount of dye CI 40 (e.g. 0.5 gram per liter) is added to provide a desired tint, the dyeing being carried out by immersion at 150 F. for a period of 5 minutes.

Following this dyeing, sealing is effected by immersion in an aqueous solution containing 10 grams per liter of ferric ammonium oxalate at a temperature of F. for a period of 4 minutes.

The resulting green coating was found to pass the con- 7 ventionalv Fade-Ometer test for a period of hours.

' The result is in sharpcontrast to the results obtained by dyeing with the same dye concentration and under the same temperature and time conditions, but with the ferric ammonium oxalate absent, followed by the same ferric ammonium oxalate seal. In the latter case, the coating stood up only for 48 hours of the Fade-Ometer test. Furthermore, while in the successful case just'described the concentration of ferric ammonium oxalate was double that in the seal and carried out at a higher the additionahs'eal was necessary for successful results,

The amount of hydrolyzable salt present in the dye bath may be considerably reduced. As an example of this, an absorbent oxide coating, produced by anodizing, was immersed in an aqueous dyeing bath containing 0.040 gram per liter of ferricammonium oxalate, and 0.2 gram per Ferric ammonium oxalate imparts a somewhat yellow or brass tint to the coating and Where this is not desired nickel acetate maybe used in the dye'bath instead of ferric ammonium oxalate. As an example of this, an absorbent oxide coating was dyed in an aqueous bath containing 13 grams per liter of nickel acetate and 2 grams per liter of the dye C1 1054, at a temperature of 120 F. for 2 minfies. This was followed by sealing in the nickel acetatesodium [fluoride-sodium dichromate seal referred'to above in Example 11 at 150 F. but for a period of only 1 minue. The resulting coating withstood the Fade-Ometer test for 300 hours. i

The concentration of nickel acetate in the dye bath may also be low as illustrated by the following example:

Dyeing was effected in an aqueous bath containing 1.0 gram per liter of nickel acetate and 0.5 gram per liter of the dye C1 1034 at 120 F. for -a period of 2 minutes. This was followed by sealing with the same seal given in Example II but sealing was effected at 180 'F. for a period of minutes. In this case, the coating withstood 300 hours in the Fade-Orneter test.

When a nickel acetate seal is used which contains a soluble fluoride, it is not necessary to include a hydrolyzable metal salt in the dye bath as shown by the following example:

Dyeing was effected in an aqueous bath containing 0.2 gram per liter of the dye Cl 1034, the oxide-coated metal being immersed in the dyebath for 2 minutes at 120 F.

Sealing was then effected by the seal given in Example TI by immersion for 5 minutes at 150 F. The coating in this case withstood 400 hours in the Fade-Ometer test.

The foregoing examples indicate that the concentrations and conditions are not critical. The concentration of dye used in the baths may vary greatly and depends primarily on the final color desired. For example, the concentration may ordinarily vary from 0.1 gram per liter to grams vper liter, but amounts outside of this range may be used depending on the intensity .the dye and the results desired.

in cases where it .is desired to use a hydrolyzable salt in the dye bath, examples of the salts used may be the weak acid salts of ferriciromferrous iron, nickel, copper, aluminum, cobalt, cadmium, zinc,'barium and lead. 'The acids involved in such salts are subject to considerable choice, and,'as examples, there maybe used thesoluble acetates, oxalates, citrates, tartrates, fluorides, chlorides and sulfates of the metals given above, and the salts may be the double ammonium salts, the latter being used primarily because of their higher stability and consequent longer lives of the baths. While when the special type of seal is used the hydrolyzable metal salt-need not be incorporated :in the dye bath, when that Seal is not used,

vor even if it is used, the hydrolyzable metal salt may have a wide range of concentration, for example, from, 0.04

' the -seal.

.. 4 gram per liter to" saturation. Temperatures involved in the dye bath treatment are not of prime importance,

though elevated temperatures of the order of F. to

160 F. may be advantageously used to decrease the time necessary for dyeing. The time required is generally a matter of minutes, for example, l/z to 20 minutes, depending entirely on the depth 'of color desired and the temperature used. l

As to the sealing, this may be carried out, when the dye bath has involved the use of a'hydrolyzable metallic salt, in a bath containing a hydrolyzable'metallic salt which may be any of the types of salts mentioned above as capable of being incorporated in the dye bath.. The sealing may be carried outin such salt concentrations and for times and at temperatures typical of conventional sealing procedures with such salts. For example, the salts may be used in concentrations ranging from 0.04 gram to saturation, temperatures may vary from 100 F. to 212 F, and times of immersion may vary from /2 to 20 minutes. Here also the salt concentrations, temperatures and times are not critical, higher concentrations and higher temperatures merely resulting in satisfactory sealing in shorter times. a

As already indicated, the sealing step is necessary even when the dye bath may contain the same hydrolyzable metal salt as is used for sealing, and even though the conditions of concentration of the metal salt in the dye bath and the temperature and time of dyeing are such that, in the absence of dye, sealing of the coating might be expected. I do not know the reasons for this, but it appears essential for satisfactory results that a separate sealing step should be involved.

When the special nickel-chromate-fluoride seal is used it is not required that a hydrolyzable metallic salt should be present in the dye bath. The preferred sealing bath, as indicated above, comprises 8 grams per liter of nickel a'cetate,'0.1 gram per liter of sodium dichromate and 0.4

gram per liter of sodium fluoride in aqueous solution.

With this bath a preferred time of scaling is 5 minutes at a preferred temperature of F. or higher;

-The special seal just described may vary considerably in composition. If nickel'acetate is used its concentration 'is desirably from 0.3 gram perliter to saturation. Instead of nickel acetate the following salts may be substituted in similar concentrations:

Acetates, citrates, tartrates, fluorides, sulfates, oxalat'es and chlorides of nickel, cobalt, iron, zinc, cadmium, barium, copper, aluminum and lead.' V

The sodium diehromatemay be eliminated entirely or it orother soluble chromates or dichromates may be used in concentrations up to 1.0 gram per liter. Since only the chi-ornate ion is involved, there may be used directly the chromate of the hydrolyzable metal involved. The pH of the sealing bath should be about 4.5 to 7.5, and may be adjusted, if necessary, by the addition of otherwise inert acids or alkalies. p i

The fluoride ion is an important constituent of this sealing bath when it isto be effective in the absence of a hydrolyzable metallic salt in the dye bath. In terms of sodium fluoride the sealing bath should'contain 0.2 gram per liter to 0.5 grams per lite'rof fluoride, though equivalent aniountsof other soluble fluorides may be used, includingfluorides of nickel or other metal involved in 'What is claimed is;

1. The method of producing colored oxide coatings on aluminum and aluminum alloys comprising absorbing in such oxide coating an aqueous solution containing a minimum of 0.040 gram per liter of a hydrolyzable salt of a weak metallic base and an anthraquinone dye of the group consisting of .anthraquinone :dyes of'the mordant type, mordant acid vtype,'acid "typ'e'and metallizable type, fol

' lowedby'sealing oftheidyed coatingby treatment with an aqueous solution containing a minimum of 0.040gram per liter of a-hydrolyza-ble .salt of a-gweak metallic base.

2-. The method of producing colored oxide coatings on aluminum and aluminum alloys comprising absorbing in such oxide coating an aqueous solution containing a minimum of 0.040 gram per liter of a hydrolyzable metallic salt and an anthraquinone dye of the group consisting of anthraquinone dyes ofthe mordant type, mordant acid type, acid type and metallizable type, followed by sealing of the dyed coating by treatment with an aqueous solution containing a minimum' of 0.040 gram per liter of a hydrolyzable nickel salt.

3. The method of producing colored'oxide coatings on aluminum and aluminum alloys comprising absorbing in such oxide coating an aqueous solution containing an anthraquinone dye of the group consisting of anthraquinone dyes of the mordant type, mordant acid type, acid type and metallizable type, said solution being characterized by the absence of hydrolyzable metallic salts, followed by sealing of the dyed coating by treatment with an aqueous solution containing a minimum of 0.040 gram per liter of a hydrolyzable salt of aweak metallic base and 0.2 to 0.5 gram per liter of a soluble fluoride.

4. The method of producing colored oxide coatings on aluminum and aluminum alloys comprising absorbing in such oxide coating an aqueous solution containing an anthraquinone dye of the group consisting of anthraquinone dyes or the mordant type, mordant-acid type, acid type and metallizable type, said solution being characterized by the absence of hydrolyzable metallic salts, followed by sealing of the dyed coating by treatment with an aqueous solution containing a minimum of 0.040 gram per liter of hydrolyzable salt of a weak metallic base, a maximum of 1.0 gram per liter of a soluble chromate and 0.2 to 0.5 gram per liter of a soluble fluoride.

5. The method of producing colored oxide coatings on aluminum and aluminum alloys comprising absorbing in such oxide coating an aqueous solution containing an anthraquinone dye of the group consisting of anthraquinone dyes of the mordant type, mordant acid type,

quinone dyes of the mordant type, mordant acid type, acid type and metallizable type, said solution being char-f acterized by the absence of hydrolyzable metallic salts, followed by sealing of the dyedcoating by treatment with an aqueous solution containing a minimum of 0.040 gram per liter of a hydrolyzable nickel salt, a minimumof 1.0 gram per liter of a soluble chromate and 0.2 to 0.5 gram per liter of a soluble fluoride.

7. The method of producing colored oxide coatings on aluminum and aluminum alloys comprising absorbing in such oxide coating an aqueous solution containing an anthraquinone dye of the group consistingofanthraquinone dyes of the mordant type, mordant acid type, acid type and metallizable type, said solution being characterized'by the absence of hydrolyzable metallic salts,

followed by sealing of the dyed coating by treatment with an aqueous solution containing. 8 grams perliter of nickel acetate, 0.10 gram per liter of sodium dichromate and 0.40 gram perliter of sodium fluoride.

References Cited in the file of this patent UNITED STATES PATENTS 2,653,926 Zickendraht et al. Sept. 29, 1953 FOREIGN PATENTS 216,952 Switzerland Ian. 5, 1942 407,475 Great Britain .s Mar. 22, 1934 

1. THE METHOD OF PRODUCING COLORED OXIDE COATINGS ON ALUMINUM AND ALUMINUM ALLOYS COMPRISING ABSORBING IN SUCH OXIDE COATING AN AQUEOUS SOLUTION CONTAINING A MINIMUM OF 0.040 GRAM PER LITER OF A HYDROLYZABLE SALT OF A WEAK METALLIC BASE AND AN ANTHRAQUINONE DYE OF THE GROUP CONSISTING OF ANTHRAQUINONE DYES OF THE MORDANT TYPE, MORDANT ACID TYPE, ACID TYPE AND METALLIZABLE TYPE, FOLLOWED BY SEALING OF THE DYED COATING BY TREATMENT WITH AN AQUEOUS SOLUTION CONTAINING A MINIMUM OF 0.040 GRAM PER LITER OF A HYDROLYZABLE SALT OF A WEAK METALLIC BASE. 